Death on tap

Cryptosporidium kills AIDS victims in Dallas. Who will the pathogen claim next?

In late May, when Dallas AIDS activist John Thomas learned he was infected with a microbe called cryptosporidium parvum, he finally decided to conclude his private battle with death. Thomas had earned national respect over the last two decades for his leadership in the global battle against death by AIDS. He knew the score. For him, the arrival in his body of this single-celled parasite was the unmistakable knell of his personal endgame.

Since 1976, when cryptosporidium first surfaced as a threat to human life, it has been associated mainly with HIV-infected victims. But that may be changing, and the question is whether John Thomas' fate is a bell that tolls for us all.

Crypto, as it is usually called, is a single-celled protozoan, like an amoeba, carried in the gut of cows and deer, sometimes transported by birds, but most efficiently carried by water. Crypto was long believed not to be harmful in human beings. It was not known to have taken a single human life before 1976.

But crypto has changed. Scientists believe it may have become increasingly resistant to chlorination and other forms of disinfection. It escapes most of the commonly used water filtration systems. And it seems to be broadening the number and types of human beings it can attack.

In 1993, cryptosporidium took root in the public drinking-water system in Milwaukee and caused the largest waterborne human epidemic in America this century, severely sickening 400,000 people and killing more than 100.

Most of the fatalities in Milwaukee were people with AIDS, but not all were. The deaths also included elderly people and very young children, and the very sick included people of all ages and descriptions.

The Milwaukee outbreak was blamed at the time on unusually low water levels, high turbidity or murkiness of the water, and mistakes made in the filtration process. But later studies threw doubt on those explanations, showing that the Milwaukee drinking-water system was meeting all federal standards when the outbreak occurred.

Tests by the U.S. Environmental Protection Agency laboratories eventually showed that the strain of crypto in the Milwaukee outbreak could actually live in pure Clorox bleach.

Since then, the U.S. Centers for Disease Control in Atlanta has logged a succession of smaller outbreaks around the nation, including one in Las Vegas in 1994 that took 39 lives, all associated with HIV infection.

In July 1993, 35,000 residents of New York City had to boil their water because of a crypto invasion of the water system. That same year, residents of Washington, D.C., and suburban Virginia had to boil water for the same reason.

Erik D. Olson of the Natural Resources Defense Council, speaking in Dallas last week, said data from the U.S. Centers for Disease Control indicate that approximately one million Americans a year are falling sick from waterborne diseases, including cryptosporidiosis. The Natural Resources Defense Council estimates that 900 a year are dying.

Some of the outbreaks have been traced to fecal contact in daycare centers and nursing homes or water contamination after water has been out of the tap. Most of the outbreaks documented by the CDC, however, have been traced to public drinking-water supply systems. About half of those systems were found later to have suffered some defect or accident that could be linked to the outbreak. But several outbreaks have been linked to water-treatment systems where everything was running smoothly.

Cryptosporidium has learned to withdraw into a hard-shelled spore that can travel and survive in chlorinated water, sea water, and fairly hot and cold water. Its normal home is in the bowels of ruminants--cud-chewing animals.

In the human gut, the spores break open and flower into a billowing plague of microbes that attach to the lining of the bowel, reproducing so fast that they literally fill a victim's insides.

There are no drug cures. The onset, once it is in full bloom, is violent and overwhelming. The only weapon against it is a healthy immune system.

A new text on crypto says, "In fact, if this parasite were not efficiently eliminated from the body, it would quickly kill an animal through dehydration and electrolyte imbalance and rapidly eliminate host species from the environment."

That means that, if crypto ever developed the ability to outwit healthy immune systems, it would eliminate human life on the planet.

As it is now, in all susceptible species other than humans, only the newborns die because their immune systems have not had time to mature. In humans, where immune failure can occur at any age, crypto attacks and kills all generations.

Terry Stewart, director of the Dallas Water Utilities, denies emphatically that crypto is carried in Dallas drinking water and says his assertion is backed by scientific test data. After a delay of several days, he produced a table of test findings that showed no crypto in "finished" or treated water in Dallas. But Dallas tests for crypto only once a month. The United Kingdom recently went from testing every 24 hours to continual testing, because crypto is so hard to find. Stewart admits there is crypto in the water coming into Dallas' treatment plants, but he did not provide data to show how much. On these findings, he asserts that Dallas is totally crypto-free.